Vehicle gasoline engines are classified into multi-port injection (MPI) engines and gasoline direct injection (GDI) engines according to their fuel injection method.
In a GDI engine, fuel stored in a fuel tank is supplied to the engine by a low-pressure fuel pump. The low-pressure fuel supplied to the engine is compressed into high-pressure fuel by a high-pressure piston fuel pump, and is then supplied to a fuel injector through a high-pressure fuel line and a fuel rail.
The fuel injector of the GDI engine is configured to directly inject the high-pressure fuel, pumped under a high pressure, into a cylinder. The fuel of the GDI engine is converted into high-pressure, fine injected particles engine and directly injected into the cylinder by the fuel injector. The injected fuel is exploded through the ignition of an ignition plug, and thus the fuel is completely combusted. Accordingly, the GDI engine is an engine which is capable of preventing atmospheric and environmental pollution because fuel combustion efficiency is high and completed combusted engine exhaust gas is discharged.
Recently, a high-pressure GDI engine in which fuel pressure is equal to or higher than 350 bars has been developed. The high-pressure GDI engine includes a high-pressure piston fuel pump, i.e., a high-pressure generator, a high-pressure fuel line, a fuel rail, and a fuel injector.
In the high-pressure GDI engine, fuel pressure is about 35 bars during low-speed idle driving, and fuel pressure ranges from 35 to 350 bars during high-speed driving.
Such a high-pressure GDI engine requires a high-pressure piston fuel pump in which the range of fuel pressure variation is 10 or more times. High-pressure fuel is obtained and also a pump pulse wave having a large amplitude is generated by the high-pressure piston fuel pump. Furthermore, when high-pressure fuel injection is performed via the fuel injector, a fuel injection pulse wave is generated inside a fuel rail.
Accordingly, mixed pulse waves in which a pump pulse wave and a fuel injection pulse wave are mixed together and which have a large amplitude are present inside the fuel rail.
When mixed pulse waves having a large amplitude are directly transferred to the fuel injector, the amount of fuel injected varies every moment. Due to variation in the amount of fuel injected, fuel is incompletely combusted, and thus engine combustion efficiency is reduced due to the incomplete combustion. Due to the incomplete combustion of fuel, the discharge of engine exhaust gas to the atmosphere causes atmospheric and environmental pollution, and mixed pulse waves cause the generation of the vibration and noise of an engine.
For the above-described reasons, there is required a wide pressure range pulsation reducer which is capable of reducing mixed pulse waves over a wide pressure range.
Conventionally, an orifice is installed at a fuel rail entrance, and reduces high-pressure pulse waves. The pulsation reducer using an orifice uses a method in which the fuel rail entrance is rapidly reduced to a size which is 1/10 or less times the section of a high-pressure fuel line, and thus the flow rate and pressure resistance of fuel are generated, thereby reducing pulsation waves.
Although the above-described pulsation reducer using an orifice can reduce a pump pulse wave, it cannot reduce a fuel injection pulse wave which is generated inside the fuel rail. Furthermore, the method using an orifice generates high pump loss (the high flow rate and pressure losses of the high-pressure piston fuel pump) because it uses fuel resistance.
Furthermore, Korean Patent No. 10-1168591 discloses a pulsation reducer using a disk spring. The pulsation reducer uses a single disk spring, and has the disadvantage of having insufficient performance in term of a reduction in pulsation over a wide pressure range, unlike a GDI engine.
Furthermore, Korean Patent No. 10-1424994 discloses a pulsation reducer using a composite disk spring. In the pulsation reducer, a piston is connected to a composite spring, and reduces pulsation. The pulsation reducer is a pulsation reducer using an indirect contact method in which pulse waves within fuel are transferred to the composite spring through the piston.
The pulsation reducer is configured such that pulse waves within fuel come into contact with the piston and pulse waves do not come into direct contact with the composite spring. The pulsation reducer has a low reaction speed when reacting to high-frequency pulse waves, and thus has the defect of not reducing high-frequency pulse waves within fuel, unlike a GDI engine.
Furthermore, the pulsation reducer has a disadvantage in that it can reduce only fuel pulse waves of an MPI engine using a single layer double-sided waveform spring over a pressure range of 4.5 bars.